Conventional arm-wrestling devices may be classified roughly into three types according to the means of providing reaction force against player's arm-force. First type is to make use of spring force, and a typical example of this one is U.S. Pat. No. 3,947,025, in which the arm-wrestling exercise device is comprised of a helical coiled spring that has adjustable stiffness as shown in FIG. 1a. Other examples of this type are U.S. Pat. Nos. 6,652,428; 5,458,554; 5,431,616; 4,900,019; 3,662,602; and Russia Patent No. 2,128,539. As a similar one with this type, there is China Patent 2691654, in which the system is weight-loaded.
The second type of arm-wrestling devices uses pneumatic or hydraulic cylinders, which is better than the previous spring type from the viewpoint of force manipulability, however disadvantages of this type are that the system becomes complicated and bulky because of the supplementary devices for pneumatic or hydraulic pressure generation, and so possibly becomes expensive. The typical inventions of this type are U.S. Pat. No. 5,842,958 as shown in FIG. 1b and U.S. Pat. No. 4,805,900 as shown in FIG. 1c. Some other inventions of this type are U.S. Pat. Nos. 3,400,793; 4,406,454; 4,754,964 and Japan Patent Publication No. 55-54969.
The third type of arm-wrestling devices uses electric motors instead of springs or pneumatic/hydraulic cylinders in order to generate resistive force against the user, and most of recent arm-wrestling devices are included in this type. The typical invention of this type is Japan Patent Publication No. 06-315544 as shown in FIG. 1d, in which a torque motor is used for generating arm force, and a sensor plate and a photosensor are used for detecting arm speed in order to prevent a throw fracture of a player. Another example of this type is Japan Patent Publication No. 54-161436.
However the foregoing devices are invented for playing simple arm-wrestling games or practicing strength training, in which they usually generate fixed force levels (that are selectable via buttons or other means). If a player generates a bigger force than the arm-wrestling device, then he will win, and, otherwise he will lose the game. Therefore, it has a deficiency that the player is soon bored with the arm-wrestling device after a few trials.